The present invention relates to an apparatus comprising a platen capable of moving in a plane, this platen being especially intended to carry microfiches. It particularly relates to the means making it possible to bring a specified microview on the platen into position opposite the optical system of the apparatus, without manual intervention by the user.
The invention also relates to the use of such an apparatus as a microfiche reader, and is described hereinafter with more particular reference to a microfiche reader.
In microfiche readers, the microfiches are arranged on the platen of the apparatus between two glass plates. This platen is capable of moving in a plane along an infinity of trajectories resulting from the movement of the platen in two rectilinear intersecting directions, these movements making it possible to place a chosen microview opposite the optical system of the apparatus.
The movements of the platen in each of the two intersecting directions are generally produced by two motors, one of the motors being usually fixed and the other being movable relative to the base and to most of the apparatus. Typically, in a conventional microfiche reader, each arrangement for movement of the platen in each direction comprises a toothed wheel fixed at an end of a shaft of the motor and two rack bars with teeth which intermesh with those of the toothed wheel. One of these rack bars is permanently attached to the platen, while the other, which picks up the play between the teeth of the fixed rack bar and of the toothed wheel, is applied against the teeth of the toothed wheel with the help of at least one spring.
In use, it proves difficult to obtain complete coincidence between the rotation of the motor and the movement transmitted to the rack bar attached to the platen, and it is therefore difficult to control the movement of the platen and consequently the position of the individual microviews.
Furthermore, the fact that one of the motors is movable relative to the whole of the reader implies that the space required for its movement must be provided in the apparatus, which increases the bulk of the apparatus.
Moreover the weight of this motor which is mounted on a movable part of the apparatus requires a reinforcement of this mobile part, resulting in an addition to the weight of the movable part. Besides, the mobility of the motor complicates its electrical supply.